EARLY STAGES IN DEVELOPMENT OF BALANOGLOSSUS. 159 



Fig. 28. — Through the ends of tlie posterior horns of the anterior body 

 caFJty, whose cavities are not prolonged to this point. In this section the 

 rudiment of the nervous system is sliown. 



Fig. 29. — Section between the anterior and middle mesoblastic regions. 



Fig 30. — Section tlirough the junction of the second body cavities and the 

 archenteric cavily. 



Fig. 31. — Section through the middle of the second body cavities. 



Fig. '61a. — Part of a section similar to the preceding. It represents the 

 minute structure of the epiblast and hypoblast, and of the mesoblastic cells 

 lining the second body cavity, which are here still connected with the hypo- 

 blast. (Obj. F, oc. 2.) 



Fig. 32.— Section through the region between the second and third meso- 

 blastic tracts. 



Fig. 33.— Section through the anterior region of the third mesoblastic 

 tracts. 



Fig. 3i. — Section taken rather behind the preceding, traversing the 

 foramina by which the posterior body cavities open to the archenteron. 



Fig. 33. — A longitudinal median section of a larva between Stages D and 

 E, showing the opening of the anterior body cavity into the archenteron. 

 (Obj. C, oc. 2.) 



Fig. 36. — Longitudinal nearly median section, almost in the vertical plane, 

 through a larva between Stages E and F. (Obj. C C, oc. 2.) The anterior 

 body cavity is now seen to be closed. 



Fig. 37. — Transverse section through the mouth of a larva between Stages 

 F and G. (Obj. D, oc. 2.) 



Fig. 38. — Transverse section through the anterior end of the collar of a 

 larva between Stages F and G (slightly older than the preceding). (Obj. D, 

 oc. 2). The nervous system is shown still continuous with the skin in this 

 region. 



Fig. 39. — Transverse section through the same larva as Fig, 38, taken 

 somewhat behind the section there represented. (Obj. D, oc. 2.) The 

 nervous system is here detached from the skin, to become continuous with it 

 again posteriorly. 



Fig. 40. — A diagram representing the arrangement of the parts as seen in 

 a median horizontal longitudinal section through a larva at Stage E. In this, 

 as in Fig. 41, the epiblast is of the medium shade, the hypoblast dark, and the 

 mesoblast light. 



Fig. 41. — Diagram of a longitudinal vertical section through a larva between 

 Stages F and G. The letter Z) indicates the dorsal side ; shading as in Fig. 40. 

 The anal perforation is here represented in order to show its eventual position. 

 It would not, however, be found until Stage G is reached. The relations of 

 the closed praeoral body cavity and of the nervous system to other structures 

 are here shown. 



